FDX-B Animal Identification Protocol description.

FDX-B
protocol is a common format used in transponders in applications
requiring animal identification, but
is also often used in non animal related industrial identification. It
is fully described in the ISO 11784 & 11785
standards publicly available. The description of ISO 11784
& 11785 discuss two forms of transponder
encoding, and these are FDX-B (full duplex), and HDX (half duplex).
Here we will discuss the FDX-B
protocol description. For a description of HDX protocol see HDX Animal
identification protocol description.

FDX-B
frequency and modulation.

FDX-B protocol based transponders are defined to operate in the
134.2kHz band, and employ a biphase
encoding scheme to transmit their information. The data bit rate
used is always fc/32.

Biphase
encoding schemes modulate the RF field so that there is a transition at
the beginning of each bit
boundary. A logic 0 state has a transition
in the
middle of the bit period, while a logic 1 state has no
transition
during the entire bit period. For FDX-B 1 bit length corresponds to 32
cycles of the activated field of the reader.

FDX-B
data structure.

FDX-B protocol based transponders carry 128 bits of data. The structure
of this data consists of:

11 header bits (10000000000) Lsb
bit first.

64 identification bits with 8 control bits.

16 bits of CRC with 2 control bits.

24 bits of extended data with 3 control bits.

The control bits are simple logic 1 bits that appear after every 8
bits. They are used to differentiate the
11
bit header from the remaining data. Below is shown an example of the
FDX-B data structure.

msb

lsb

1

0

0

0

0

0

0

0

0

0

0

Header pattern. 11 bits.

1

1

1

1

1

0

0

0

0

1

0

0

0

0

0

0

1

1

38 bit (12 digit)
National code.

1

0

0

0

0

0

0

0

0

eg.
000000001008 (decimal).

1

0

0

0

0

0

0

0

0

1

1

1

0

0

0

0

0

0

10 bit (3 digit) Country
code.

1

1

1

1

1

1

0

0

1

eg. 999
(decimal).

1

-

-

-

-

-

-

-

1

1 bit data block status
flag.

1

1

-

-

-

-

-

-

-

1 bit animal application
indicator.

1

1

1

0

1

0

1

1

0

16 bit checksum.

1

0

1

0

1

1

1

0

1

1

0

1

0

1

0

1

1

0

24 bits of extra data if
present.

1

0

0

1

1

0

1

0

0

eg. $123456.

1

0

0

0

1

0

0

1

0

When the Tag enters the electromagnetic field transmitted by the RFID
reader it draws power from the field
and will commence transmitting its data as shown above with the least
significant bit (lsb) first. The 11 bit
header pattern is transmitted to indicate the beginning of the data
block.

This is followed by 38 bits of the identification code. For an animal
application this will be the identity code of
the animal. This is a unique 12 digit decimal code for each
animal.
After every 8 bits is sent a logic 1 bit is inserted to
differentiate data from the header sequence.

This is followed by the 10 bit country code. A country code is
a 3 decimal digit value used to refer to
individual manufacturers. A code of 999 is used to indicate that the
transponder is a test transponder and
need not contain a unique identification number.

The 1 bit data block status is an indicator flag to indicate whether an
additional data block exists. A value of 1
indicates that the transponder contains an additional 24 bit data
block. Otherwise it is 0. Following this we
have 14 reserved bits allocated for future use.

The animal application indicator is a single bit indicating
that the
transponder is used for animal identification.
This value is set to 1 to indicate an animal identification
application, and 0 otherwise.

The preceding 64 bit block (excluding control bits) is then used to
calculate a 16 bit checksum. The calculation
for this CRC checksum is defined in ISO 11784
& 11785 and is included after the animal status bit.

After the CRC check bits we have the extra data block. This data block
exists if the data block status flag is 1.
When the data block status flag is 0 this value will
be 000000. The data block may be used to append
additional data relevant to the individual application.